Two leading telecom firms, Bharti and Vodafone, have come under the scanner of regulator Trai for violating Mobile Number Portability (MNP) norms.

Trai had issued showcause notices to these firms seeking information based on complaints from subscribers that their requests for MNP have been rejected, sources in the know said.

"We have received their (Bharti and Vodafone) replies and the same is under examination. After analysing it we shall decide the next course of action," sources in the Trai said.

Trai has investigated rejection of MNP requests by various service providers by sending a team of its officers to telecom operators' offices, they said, adding that the matter has been brought to the notice of the Telecom Ministry also.

"The DoT may also take necessary action at their end," the source said.

According to the data available with Trai, so far 893 MNP requested have been rejected by operators.

The Telecom Regulatory Authority of India (Trai) had issued a directive to all cellular mobile telephone service providers and unified access providers on December 3, 2010, prohibiting charging extra for SMSes sent to '1900', the number for availing the MNP service.

Regarding outstanding payments from subscribers availing the MNP service, Trai recommended that if the unpaid amount in the previous bill is less than Rs 10, the service provider may include the same in the subsequent bill of the subscriber without any penal charges.

In order to reduce the number of porting rejections by service providers, Trai had issued directions to the service providers on May 24, 2011, specifying that rejection on the premise of contractual obligation can be done in case of post-paid connections with bundled handsets, or corporate connections, which have an exit clause that has not been complied with by subscribers.

MNP service was made nation-wide from November 25, 2010, that allowed cellphone users to switch operators without changing numbers.

As per the eligibility criteria for MNP, customers are required to have cleared all of their outstanding bills before making an application, the Department of Telecom (DoT) said.

The one-time charge that needs to be paid by subscribers would differ from operator-to-operator, but the charge cannot exceed Rs 19, the DoT had said.